To clarify whether the excitation energy transfer from a donor molecule or aggregate to a remote acceptor molecule or aggregate can be caused by nonadiabatic interaction as expected in our previous studies (Okuno, Y. Chem Phys Lett 2001, 347, 138 -142; Okuno, Y.; Mashiko, S. Int J Quantum Chem in press), we carried out ab initio calculations for three donor-acceptor systems. Even when the acceptor is separated from the donor by 15 , it was found that nonadiabatic coupling elements have moderately large values in the nuclear-configuration region where the potential energy surfaces at two excited states for the donor-acceptor system are close to each other, otherwise the conical intersection between the two excited-state potential energy surfaces appears. In addition, it was found that the adiabatic approximation for the donor-acceptor system holds in the nuclear-configuration region where the initial and final wave packets in the process of the excitation energy transfer lie in. These findings lead to the conclusion that the excitation energy transfer between two remote molecules or aggregates can be caused by the nonadiabatic interaction.

DOI:10.1002/qua.10579